The present invention relates to a fibre-optical strain gauge of the kind set forth in the preamble of claim 1.
In fibre-optical gauges of this kind it is known to incorporate a mechanical construction which provides a relative movement of oppositely positioned spaced apart first and second optical fibre ends in a direction substantially perpendicular to the axial direction of the optical fibres and using the varying transmission of light between the two fibres as an indication of the parameter to be measured. A fibre-optical gauge of this kind is known from U.S. Pat. No. 4,300,813 and although this document does not describe a strain gauge, the document is taken as a starting point for the present invention.
It is the object of the present invention to provide a fibre-optical strain gauge of the kind referred to above, with which it is possible to provide strain gauge measurements which are substantially not influenced by movements of the measuring points in directions in a plane perpendicular to the desired strain-measuring direction, and this object is achieved with a fibre-optical strain gauge of said kind, which according to the present invention also comprises the features set forth in the characterizing clause of claim 1. With this arrangement, said movements of the measuring points are eliminated to a large extent by means of the connecting rods comprising articulated connections at both ends, whereby such movements are substantially without influence on the further parts of the mechanical construction which transfers the movement of the measuring points in the strain-measuring direction to the fibre-holding elements. Preferred embodiments of the fibre-optical strain gauge, the advantages of which will be evident from the following description of preferred embodiments, are revealed in the sub-ordinate claims.